1. Field of the Invention
This invention relates to textile sizing compositions and textiles sized therewith.
2. Background of the Art
Sizing is the term for the procedure wherein yarn is prepared for weaving. During sizing, yarn is coated with a layer of polymers by immersing the yarn in an aqueous sizing liquor in order to diminish friction between the yarn and the metal parts of a loom used to weave the yarn into textiles. Sizing also can improve the abrasion resistance of yarn during weaving.
The main objective of sizing is to allow the weaving of yarns to be done efficiently, reducing the number of breaks and, as a consequence, the number of loom stops. Sized yarns are reinforced, smoothed and lubricated.
A sizing machine (slasher), is a machine having one or two sizing boxes in which yarn, coming from a warping beam or a creel, is immersed in an aqueous sizing solution (sizing bath or sizing liquor). The yarn is then squeezed, in a dryer, using several hot cylinders to eliminate the excess liquor. The dryer also includes a winding unit where the sized yarn is wound onto a beam for eventual loading on a loom to be woven into a textile. Sizing can be performed with a xe2x80x9cback beamxe2x80x9d system in which several beams are sized at the same time, or with a xe2x80x9cbeam to beamxe2x80x9d system wherein a single beam is sized.
Sizing compositions generally should be easily dispersible in water without foam formation and should produce a sizing liquor having a desired viscosity. Once dried, sizing compositions should form a thin and soluble film on yarn, which is easily removed by washing or scouring from the textile (fabric). One problem with conventional sizing compositions is that they must be removed from the sized fabric to enable an efficient finishing, and thus a large quantity of waste compositions with a high content of pollutants can be discharged into the preparation mills"" water, which can result in significant costs for water treatment.
Starch derivatives are widely used in yarn sizing and they are often the main constituent of many sizing compositions. The starch derivatives are usually used together with synthetic polymers such as polyvinyl alcohol and/or with modified natural polymers such as carboxymethyl cellulose, especially where a high film strength is required. One disadvantage of starch derivative sizing compositions is that they may require enzymes for efficient removal, which can increase costs associated with their use. It would be desirable in the art of sizing textile to reduce the xe2x80x9cadd-onxe2x80x9d (quantity of sizing on the yarn), the production costs and also the pollution in waste water resulting from sizing operations.
In one aspect, the present invention is a sizing composition for use with open-end yarn comprising from about 20 to about 100 percent, by weight, high viscosity cellulose ethers having a molar substitution of from about 0.5 to about 4.0.
In another aspect, the present invention is a sizing liquor for use with open-end yarn comprising from 0.5 to 5 percent by weight of high viscosity cellulose ethers having a molar substitution of from about 0.5 to about 4.0 and having a viscosity of from about 100 to about 1000 cps at 85xc2x0 C.
In yet another aspect, the present invention is a sized open-end yarn comprising an open-end yard sized with a sizing liquor comprising from 0.5 to 5 percent by weight of high viscosity cellulose ethers having a molar substitution of from about 0.5 to about 4.0 and having a viscosity of from about 100 to about 1000 cps at 85xc2x0 C. and having an add-on of between about 0.8 and about 6 percent by weight.
Another aspect of the present invention is a process for sizing open-end yarn comprising sizing an open-end yarn using a sizing liquor comprising from 0.5 to 5 percent by weight of high viscosity cellulose ethers having a molar substitution of from about 0.5 to about 4.0 and having a viscosity of from about 100 to about 1000 cps at 85xc2x0 C.
In still another aspect, the present invention is a sizing composition for use with open-end yarn comprising from about 20 to about 100 percent, by weight, high viscosity cellulose ethers having a molar substitution of from about 0.5 to about 4.0.
While all kinds of yarn can be sized, the present invention is directed particularly to the warp sizing of natural, artificial, synthetic or blended staple fibers coming from an open-end spinning, the so called xe2x80x9copen-end yarnsxe2x80x9d. Open-end yarns (or rotor yarns) are generated by a non-conventional spinning system in which the sliver feedstock is highly drafted, ideally to individual fiber state, thus creating an open end or a break in the fiber flow. The fibers are subsequently assembled on the end of a rotating yarn and twisted in.
The resulting yarn appears regular and well built, but the longer fibers may twist around the yarn and impart to the yarn its characteristic hairy aspect. The open-end spinning is an alternative to the traditional ring spinning wherein the yarn is produced through the steps of drawing, twisting and winding in a continuous way. The open-end yarn compared to the traditional (or ring yarn) has different tensile characteristics, particularly a lower breaking point, a lower tenacity, a higher stiffness, and a better abrasion resistance.
The viscosity range of sizing liquors of the present invention is usually 50-250 centipoises (cps) at an operating temperature of from about 70 to about 90xc2x0 C. For the purposes of the present invention, the term xe2x80x9cviscosityxe2x80x9d means a Brookfield viscosity, determined according to ASTM standard method D2169-99.
The quantity in weight of dried sizing composition applied on 100 part in weight of yarn (add-on) is normally comprised between 6 and 30 percent, depending on the yarn count (fineness). When performing an open-end yarn sizing operation, it is important to consider that this type of yarn is more open, more porous, more bulky, hairy and with a lower tenacity than a traditional ring yarn.
The open-end yarn sizing composition of the present invention essentially consists of from about 20 to about 100 percent by weight of high viscosity cellulose ethers having a M.S. from about 0.5 to about 4.0. For purposes of the present invention, xe2x80x9chigh viscosity cellulose ethersxe2x80x9d are cellulose ethers having a viscosity from 500 to 8000 cps at 20xc2x0 C. in a 2 percent aqueous solution. The term xe2x80x9cM.S.xe2x80x9d means xe2x80x9cmolar substitutionxe2x80x9d, namely the average number of moles of substituent added per sugar unit. The preferred high viscosity cellulose ethers of the present invention have a M.S. from about 0.5 to about 1.2.
Advantageously, the high viscosity cellulose ethers of the present invention are selected from the group consisting of carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and mixtures thereof. Particularly preferred among these cellulose ethers is carboxymethyl cellulose. The preferred high viscosity cellulose ethers of the present invention have a viscosity from 1000 to 3000 cps at 20xc2x0 C. in a 2 percent aqueous solution. When the cellulose ethers are carboxymethyl cellulose or methyl cellulose the M.S. value coincides with the D.S. value; the term xe2x80x9cD.S.xe2x80x9d means xe2x80x9cdegree of substitutionxe2x80x9d, namely the average number of hydroxyl groups per monosaccharide unit that have been etherified.
According to one aspect of the present invention, the open-end yarn sizing composition may contain one or more natural, natural-modified, or synthetic polymers chosen in the group consisting of polyvinyl alcohol, acrylic polymers and copolymers, starch, modified starch, polygalactomannans, tamarinds. According to a further feature of the present invention, the sizing compositions are normally dispersed or solubilised in water to prepare sizing liquors for open-end yarns; these liquors have a viscosity from 100 to 1000 cps at 85xc2x0 C., preferably from 100 to 300 cps, and essentially contain from 0.5 to 5 percent by weight of high viscosity cellulose ethers having a M.S. from about 0.5 to about 4.0.
According to another aspect of the present invention, the open-end yarns sized with the sizing compositions of this invention have an add-on of from about 0.8 to about 6 percent by weight. The results obtained with the sizing compositions of this invention are desirably advantageous compared with the prior art requirement of loading yarns with from 6 to 30 percent by weight of add-on. As already stated, all sizing compositions applied on yarn should be removed from the fabric before dyeing and finishing.
The sizing compositions normally contribute about 70 percent of the pollution of wastewater from a preparation mill. It is well known that all wastewater must be treated in order to reach a Chemical Oxidation Demand (COD) and a Biological Oxidation Demand (BOD) within the limits of law and a drastic reduction of oxygen request during wastewater treatment is economically very advantageous. Using the sizing compositions of the present invention, the add-on can be reduced by from 60 to 80 percent and a COD reduction of 70 percent can thus be expected. This is an excellent result both from a technological and from an economic point of view.